You may remember that quite a while ago an FD-PCP failed, with the air tube departing the rest of the rifle and disappearing like a missile.... The tube has just been recovered, and here are photos of the threads....





You will note that the tops of the threads are truncated, and the OD, when measured, was 0.014" below the minimum tolerance for that thread size.... If the receiver threads were at the maximum permitted ID, that only left 0.005" of thread engagement.... There seems to be little doubt that is why it failed....

Bob